Using Parts Galore mod, You can create powerful armor against Rail guns, If you don't want shields...
In The picture shown, Two railguns with the same power attack normal armor (left) and Light armor (Right)
Lets see how it does against a powerful rail. "Mercy"
"Mercy" has over 2000% (I'm assuming that number is damage boost?)
It Shreds through Normal armor, While being stopped by Light armor.
The Light armor is half the cost of normal armor, With half the health.
Heavy armor works the same as Light armor when tested.